1. Field of the Invention
The invention relates generally to electrocardiography systems. More specifically, the invention relates to an ambulatory ECG analysis system for manipulating and analysis of analog and digital ECG data.
2. Prior Art
ECG analysis systems are used to record and analyze characteristics of the electrical signals generated by a patient's heart, often over an extended period of time. Analysis over an extended period is usually performed in conjunction with a recorder which collects information from the patient related to the patient's ECG over a predetermined period, and stores the information for later evaluation. An analyzer, often referred to as a "scanner", is then used to analyze the collected information. Scanners usually include a playback deck for downloading information from a cassette tape obtained from the recorder, and a processing unit such as a computer, for analyzing the data and recording and editing the results. The scanner may also include a monitor for allowing the physician to display data for review, and/or a printer for allowing hard copies of data and analysis reports to be made.
It has become increasingly important for scanners to be automated in order to limit the time in which it takes to process, analyze, and report data to the physician. Further, it has become increasingly important to increase the accuracy of the data collected and the data analysis methods in order to allow more thorough diagnosis to be performed.
Prior art ECG recorders are generally designed for portable, long term detection of ECG signals from a patient over an extended monitoring period. The recordings made are subsequently used to detect abnormalities in the heart's electro activity caused by routine daily activity, or heightened emotional or physical states. The recordings are studied and reviewed to form diagnoses, such as the efficacy of drug therapy treatments or heart pacemaker performance.
ECG analyses have historically been performed in three different ways: 1) Technician analysis; 2) Retrospective analysis; and 3) Real-time analysis.
Technician analysis requires a highly skilled person to perform a visual and audio review of the ECG data as it is displayed on a monitor at high speeds. The monitor superimposes the ECG wave forms on top of each other at a very rapid pace, such as 120 times faster than real-time, with a audio signal being produced in conjunction with each beat. The technicians analysis includes detection of variations in sound and position of abnormal signals from the more common sound and position pattern of the majority of "normal" heart beats. The technician then saves and prints representative strips of ECG data which includes the abnormal ECG wave forms. The technician also often writes a summary document for the entire monitoring period which outlines the particularly noted abnormal ECG events.
Retrospective analysis of ECG data only occurs after the completion of the entire heart monitoring period. Commonly, the ECG data has been previously collected on a recording medium such as a cassette or reel to reel tape and downloaded into the analysis system at a very high speed, such as 60 to 240 times faster than real-time. In retrospective analysis, the analog ECG data taken from the tape is converted into digital format before analysis, editing, and reporting of the collected digital data is performed. During analysis, the technician is often allowed to define the parameters used to detect beat abnormalities if desired.
Although retrospective analysis offers significant time savings to a physician or technician over technician analysis, there are still significant time and position interface requirements involved in the use of retrospective analysis. Typically, to make use of the entire body of data collected on the tape, the entire tape must be converted into digital format and downloaded into the retrospective analysis system. This requires at least one pass of the entire tape, and often a second entire pass before analysis, editing and report records can be generated. Then, after analysis is complete, the digital signals must be converted back to analog for graphic printout of the ECG wave forms. The analysis process can therefore consume a full hour of the physician's time before a final report of a complete monitoring period can be generated.
Further, the accuracy of reports generated through retrospective analysis are very much dependent on the physician's or technician's knowledge of ECG analysis systems and his or her ability to correctly set parameters for abnormal ECG waveforms, and for arrhythmia and ST segment level detection and measurement, and so forth. Even though the analyses themselves may be automated or manually carried out, the results are nevertheless considered to be relatively subjective.
Real-time analysis (RTA) includes the use of a processor and solid state memory to keep pace with the ECG data as it is collected by the recorder during the monitoring period. At the completion of a monitoring period, the data is transferred to a real-time analysis system where it is processed to allow storage, retrieval and report generation. Further, in some real-time analysis systems, a limited amount of editing is also possible. Physician and technician time involved in real-time analysis is very minimal.
A major drawback with real-time analysis systems is that the recorder is generally limited in the amount of data it can store during the monitoring period. It has therefore been necessary for prior art recorders to be designed to either "compress" the monitoring period data into its solid state memory, or to "selectively store" only abnormal ECG data. In the first case, "compressed" data often results in significant shape distortion of the ECG signals and only allows "abbreviated" ECG signals to be retrieved. When the complete ECG data is later printed by the real-time analysis system, gaps will appear between samples of ECG data, thus reducing the accuracy of the report, and distorting the shape of the ECG waveforms.
Alternatively, the recorder may be designed to "selectively store" only abnormal ECG data in order to avoid the necessity of compression. However, full disclosure (FD) capability is subsequently lost, or shown only in analysis as trends, graphs, histograms, and numerical summaries, all being limited to statistical data which cannot be verified.
There therefor exists a need in the art to develop a real-time analysis system which continuously performs digital real-time analysis of ECG signals while simultaneously continuously records the ECG signals in analog format on tape for future full disclosure. There further exists a need in the art to develop a system including tape recording of analog ECG data which allows rapid full disclosure summary report generation with minimum physician/technician interface.